Sunday, July 21, 2013

Believe it or not, a "smart" brain is not necessarily a healthy brain. Nevertheless, if Einstein had worked out regularly and lived a couple of years (better decades ;-) longer, he may have had a change to figure out the missing link between his Theory of Relativity and the Quantum Theory ;-)

"Workout for your brain!" If you were a member of the club of sedentary couch-potato, you would probably be thinking of Dr. Kawashima or similar IQ games on one of your beloved gaming devices. As a diligent student of the SuppVersity and life-long follower of physical culture, you will yet be aware that the imperative "Work out for your brain!" has to be understood quite literally. After all, there have been dozens of studies to show how exercise benefits the brain of young and old, sick and healthy, lean and obese individuals.

In this context scientists often measure a peptide that goes by the name brain-derived neurotrophic factor, or short BDNF, which has been recognized as an important tropic hormone in the regulation
of neuron morphology and survival. With exercise being one of the stimuli that triggers its production BDNF it is not surprising that working out has been shown to improve cellular development and growth, exert beneficial effects on mood regulation, and cognitive functions such as learning and memory - all of these things are after all influenced by this important hormone.

Low circulating BDNF levels, on the other hand, have been associated with a widerange of neuropsychiatric disorders including depression (Karege. 2002), bipolar disorder (Cunha. 2006), schizophrenia (Zhang. 2007) and neurodegenerative diseases (Yu. 2008). And despite the fact that a definitive causal relationship between low BDNF levels and the said pathologies has yet not been established, researchers are confirmed that elevated BDNF levels can lead to improved brain health.

So if exercise is good, how much is optimal?

As mentioned before, we do already know that chronic exercise training - endurance exercise in particular - will promote the production of this important neurologically active peptide, what we do not know, however, are the dosage and intensity that would yield "optimal" effects... well, I should say we did not know that until a group of researchers from the Department of Psychology, Neuroscience Program, and the Department of Health Promotion and Human Performance at the Weber State University in Odgen gave us a first glimpse on what this "optimal" dose / intensity ratio may look like.

In their latest paper Matthew T. Schmolesky, David L. Webb and Rodney A. Hansen report the results of a study involving 45 healthy human adult males aged 18-25, who were assigned to one out of six exercise conditions that varied in both, intensity (80% or 60% of heart rate reserve, or control) and duration (20 or 40 min). To elucidate whether circadian or other effects would influence the response to the long and short vigorous and moderate intensity exercise, three subjects were excluded to serve as a sedentary control.

If you discard the inter-group differences and focus on the effect size in general, first, you will notice that any type of aerobic exercise will result in significant increases in BDNF levels (30% on average). Once you look closer, it does yet become apparent that there is a non-significant tendency for higher changes in BDNF levels with higher intensities and longer durations.

For the study at hand this implies that the Vig40 trial, in the course of which the subjects cycled for 40 min at an intensity of 80% of their maximal heart rate, yielded the greatest total increase in BDNF. If you do yet take a look at the non-significant difference to the Vig20 trial, the additional 25% increase in BDNF is paid for with an additional 20 minutes on the cycle ergometer. Now taking into account that this was still more effective than the high dose bout (40min) of moderate intensity exercise, the 20 min of vigorous exercise provide the most BDNF-bang for your bucks and should thus be considered the "optimal" training regimen to promote your brain health.

"Hold on that's not optimal"... Ok, you are right, it is not just questionable, but in fact highly unlikely that the scientists actually found these 20 minutes of vigorous activity are actually the non-plus-ultra among the unlimited number of potentially BDNF-boosting exercise regimen.

In fact, the existing bias towards higher intensities and shorter durations. Yet while this would suggest that high intensity interval training could be the true "optimum" in terms of BDNF-boosting exercise. There are as of now no human studies to support this notion and a previously published study in which the researchers tested the effects of exercise on the regeneration of axons in injured peripheral nerves clearly suggests that the BDNF response to interval training is inferior to its continuous counterpart (Wood. 2012).

Whether these results are applicable to human beings and / or whether the 5x2min intervals the rodents in the Wood study were exposed to may have been "too much of a good thing", will yet have to be elucidated in future trials.

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